1. Field of the Invention
The invention relates to an inductor and more particularly to an inductor device with multi-layered interconnections.
2. Description of the Related Art
As shown in FIG. 1, for a 0.35-μm silicon process, a silicon oxide layer 3 is disposed on a p-well layer 2 on a silicon substrate 1. Three metal layers M1, M2, and M3 are embedded in the silicon oxide layer 3, and the top metal layer M3 is exposed on an upper surface of the silicon oxide layer 3. A silicon nitride layer 4 covers the silicon oxide layer 3 and the metal layer M3. The metal layer M3 is the thickest of the three metal layers M1, M2, and M3, and thus, the conductivity thereof is higher than the other two metal layers. Further, the metal layer M3 also comprises a conductor loss lower than those of the other two metal layers. As a result, the metal layer M3 is suitable for RF (radio frequency) low-loss component designs.
FIG. 2 is a top view of a conventional three-turn inductor 5. The magnetic flux is largest on the innermost turn 6 of the inductor 5, and thus, the induced eddy current on the innermost turn 6 causes the current density of the innermost turn 6 to be very non-uniform. That is, the current that is flowing concentrates at the inner part of the innermost turn 6, and the effective cross-section for the current flow slashes, negatively affecting the performance of the inductor 5 and reducing the quality factor (Q value) thereof. Further, when the frequency of the electronic signal becomes higher, the inductor 5 suffers more negative influence to the quality factor.